Pump



May 8, 1962 Filed July 6, 1959 J. PSCHUNDER PUMP 2 Sheets-Sheet 1 INVENTOR BalphJPsshunder ATTORNEYS May 8, 1962 R. J. PSCHUNDER} 3,033,119

PUMP

Filed July 6, 1959 2 Sheets-Sheet 2 2,6 3 6 I I I 6 16 4'5 '7; 7 J3 5 5 41 1 twy 0 I 1 1 16.5 Zls/ 6 6 39 44 "a" 55 35 53 1 55 AV AY ATTORNEY S United States Patent 3,033,119 PUMP Ralph J. Pschunder, Watertown, N.Y., assignor to The JNew York Air Brake Company, a corporation of New ersey Filed July 6, 1959, Ser. No. 825,056 7 Claims. (Cl. 10337) This invention relates to reciprocating piston pumps of the type wherein discharge flow from the pump working chamber is controlled by a spring-biased check valve.

The object of this invention is to provide a displacement-controlling mechanism for pumps of this type, particularly those employing opposed longitudinally recipro eating pistons, which is relatively simple and inexpensive to manufacture, reduces pressure surges, and, during minimum displacement operation, unloads the pistons and establishes a by-pass flow for cooling the pump. According to the preferred form of the invention, each pump working chamber is connected with a variable volume accumulator chamber containing a piston or movable wall which is shiftable in volume-increasing and volumedecreasing directions by a spring and by the difference between the fluid pressures in the accumulator chamber and in a biasing chamber located on the opposite side of the piston. The effective displacement of the pump is governed by the movement of the accumulator piston during the discharge stroke of the associated pump piston, and this, in turn, depends upon the pressure in the biasing chamber.

In the preferred embodiment, the invention is employed as a discharged pressure compensator (i.e., it functions to vary displacement in inverse relation to discharge pressure) and so the pressure in the biasing chambers is regulated by a control valve which is responsive to discharge pressure. When discharge pressure is below a predetermined value, the pressure established in each biasing chamber is a maximum and the accumulator piston is held in a position establishing minimum chamber volume. Under these conditions, all of the fluid displaced by the associated pump piston is delivered to the discharge port of the pump and the effective displacement of the pump is a maximum. When discharge pressure rises above the predetermined value, the control valve decreases the pressure in each biasing chamber thereby allowing the pressure developed in the accumulator chamber during the discharge stroke of the associated pump piston to shift the accumulator piston in the volumeincreasing direction. While the accumulator piston is moving, the discharge check valve remains closed and the fluid displaced by the pump piston is delivered to the accumulator chamber. Movement continues until the spring and pressure forces acting on the accumulator piston are again in equilibrium. Once this point is reached, the check valve opens and the fluid displaced during the remaining portion of the discharge stroke is delivered to the discharge port. As each pump piston moves on its suction stroke, the fluid collected in the associated accumulator chamber is returned to the pump working chamber. It will be apparent that the effective displacement of each pump piston varies in inverse relation to the distance the associated accumulator piston is shifted during the discharge stroke and that this distance depends upon the pressure in the biasing chamber. It will also be apparent that the accumulator affords a convenient means for eliminating pressure surges.

The preferred form of the invention also includes apparatus for circulating fluid through the pump housing during zero displacement operation. This mechanism comprises a by-pass port, a passage connecting this port with the accumulator, and a valve, carried by the accumulator piston, which establishes communication between the passage and the accumulator chamber only when that piston approaches its maximum volume position. With this arrangement, by-pass flow is produced at low pressure and only at the time that cooling is needed (i.e., during zero displacement operation). The feature conserves energy and consequently improves the efliciency of the pump.

The preferred embodiment of the invention will now be described in detail with reference to the accompanying drawing, in which:

FIG. 1 is an axial sectional view of an opposed piston highspeed pump incorporating the improved displacement varying mechanism; that mechanism serving as a discharge pressure compensator.

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1.

FIG. 3 is an enlarged view of a portion of FIG. 1 showing the discharge check valves and the accumulators.

FIG. 4 is an enlarged perspective view of one of the check valve stem guides. I

Referring to FIG. 1, the'pump comprises a housing 11 formed with inlet and discharge ports 12 and 13, and a by-pass port 14. The discharge port 13 communicates with an annular groove 15 which encircles the cylinder block 16. This block is pressed into a bore formed in housing 11 and contains two circular series of aligned longitudinal cylinder bores 17 and 17. Pump pistons 18 and 18' reciprocate in the bores of series 17 and 17,

respectively, and define, with the inner closed ends of these bores, variable volume working chambers 19 and 19'. Extending between each pair of aligned cylinder bores 17 and 17' is a coaxial plunger bore in which is mounted a piston plunger 21. These plungers 21 abut the inner ends of pump pistons 18 and 18'. A piston shoe 22 is mounted for universal movement on the outer end of each pump piston 18, 18'.

Extending through, but spaced radially from, an axial bore formed in cylinder block 16, is a drive shaft 23 containing an axial bore 24 and radial passages 25 and 25' which are aligned with the inlet passages 26 and 26' formed in the cylinder block 16. The shaft 23 is journalled in bearings 27 and 28 located on opposite sides of cylinder block 16 and is provided with a conventional running seal 29 at its left end. Carried by the drive shaft are two swash plates 31 and 31'; the former being an integral part of the shaft and the latter being splined to it, as shown. The cam faces 32 and 32' of these swash plates lie in parallel planes and are in sliding engagement with piston shoes 22. The piston plungers 21 are of such length that the shoes carried by the two sets of pump pistons are maintained in operative engagement with the swash plates 31 and 31.

Coaxial with the two series of cylinder bores 17 and 17' are two similar series of bores 33 and 33; there being the same number of bores in these series as in the scrim 17 and 17. One bore in the series 33 is connected with each working chamber 19 by a passage 34, and a similar passage '34 connects each working chamber 19' with one of the bores 33'. Each aligned pair of bores 33, 33' communicates with the annular discharge groove 15 through a passage 35. The check valve stem guides 36 and 36' are mounted in the bores 33 and 33 and are held in place by integral shoulders 37 and 37' and threaded sleeves 38 and 38'. These guides 36 and 36' contain axial bores 39 and 39' which receive the stems 41 and 41' of the spring-biased check valves 42 and 42'. Cross slots 43 and 43, formed in guides 36 and 36', respectively, permit hydraulic fluid to flow into bores 39 and 39' when the associated check valve is open. As each of these valves closes under the combined action of spring 44 and the discharge pressure in groove 15, the stems 41 and 41' overtravel the slots 43 and 43 thus trapping oil in bores 39 and 39 and creating hydraulic stops. This type of check valve is particularly useful in high-speed pumps and is more fully disclosed and claimed in applicants copending application Serial No. 826,057, filed July 9, 1959.

Reciprocable within the sleeves 38 and 38' are accumulator pistons 45 and 45, respectively, which divide the spaces within the respective sleeves into two chambers, namely, a biasing chamber 46, 46', located between the inner end of the piston and the bottom of the bore in the sleeve, and an accumulator chamber, located between the outer end of the piston and the stern guide 36 or 36. The accumulator chambers communicate with the passages 34, 34 by diametrically opposed longitudinal grooves 47, 47' formed in the stem guides 36 and 36'. Pistons 45 and 45 are biased to the positions shown in the drawings (in which positions the volumes of the accumulator chambers are Zero) by springs 48 and 48 and the fluid pressure in biasing chambers 46 and 46. The pressures in the biasing chambers are regulated by a control valve 49.

As shown in FIG. 1, the control valve 49 is provided with an inlet port 51 which is connected with the annular discharge groove by passage 52, an outlet port 53 which communicates with the biasing chambers 46 and 46 through branched passage 54 and annular grooves 55 and 55, and an exhaust port 56 which communicates with the inlet port 12 through the space within housing 11 surrounding bearing 28 and swash plate 31. Communication between these three ports is controlled by a valve plunger 57 which is reciprocable within valve sleeve 58 and is formed with two spaced portions 59 and 61 of reduced diameter that define two valve lands 62 and 63. Valve plunger 57 is biased to the position shown in the drawing (in which exhaust port 56 is isolated from the other two ports by land 63) by coil spring 64. The plunger is shifted to the right against the bias of this spring by the discharge pressure of the pump which is transmitted via passage 65 to the space 66 where it acts. upon the left end face of land 62. Movement of the plunger 57 to the right causes lands 62 and 63 to increase progressively the restriction to flow from inlet port 51 to outlet port 53 and decreases progressively the restriction to flow from outlet port 53 to exhaust port 56. This action has the effect of decreasing the pressure in the biasing chambers 46, 46'. A rapid rate of change of this pressure with movement of plunger 57 is ensured by including a flow restrictor 67 in the inlet passage 52.

Encircling the cylinder block 16 are two additional annular grooves 68 and 68' which communicate with the ports 69 and 69 formed in sleeves 38 and 38 and are connected with the bypass port v14 by common passages 71 and 71. The ports 69 and 69 are so located that they are overtravelled and closed by the accumulator pistons 45 and 45' when those pistons are in the positions shown in the drawings and are uncovered at some point in the travel of the pistons inward into sleeves 38 and 38'. In this embodiment, the ports 69 and 69 are opened when the pistons are approaching the limit of their movement in the inward direction.

Operation Since the pump pistons in the two series 18 and 18' and their associated displacement-varying mechanisms operate in the same manner, this discussion will be confined to the series 18.

During operation, fluid entering inlet port 12 flows into axial bore 24 in shaft 23 and is expelled, by centrifugal pumping action, through the passage into the inlet passages 26. As the pump pistons 18 move outward on their suction strokes, the passages 26 are uncovered and the hydraulic fluid flows into the working chambers 19. On their discharge strokes, the pistons 18 again close these passages and the fluid displaced by the pistons flows through the passages 34, the check valves 42, and annular groove 15 to discharge port 13.

Fluid under discharge pressure is transmitted by passage 65 from annular groove 15 to the space 66 within control valve sleeve 58 where it acts upon the left end face of valve land 62. When discharge pressure is less than a certain predetermined value, the pressure force developed at this face is iusufiicient to overcome the bias of spring 64 and the control valve plunger 57 assumes the position shown in FIG. 1. In this position, the exhaust port 56 is isolated from the inlet and outlet ports 51 and 53, respectively, and the two last-mentioned ports are interconnected by the reduced diameter plunger portion 61. This connection permits fluid under discharge pressure to flow through the passages 52 and 54 and the annular groove 55 to the biasing chambers 46. The check valve springs 44 are preloaded slightly more than the accumulator springs 48 so that when the biasing chambers 46 are subject to full discharge pressure, each accumulator piston 45 is held in its minimum volume position (as illustrated) against the back pressure in passage 34 throughout the entire discharge stroke of the associated pump piston 18. As a result, all of the fluid displaced by the pump pistons 18 passes through the check valves 42 and is discharged from the pump through port 13.

When pump discharge pressure exceeds the certain predetermined value, the pressure force acting on the left end face of land 62 shifts valve plunger 57 to the right against the bias of spring 64. This movement causes land 62 to restrict progressively the interconnection between ports 51 and 53 and to open progressively communication between ports 53 and 56 with the result that the pressure in passage 54, annular groove 55, and biasing chambers 46 decreases. When this happens, the force developed at each accumulator piston 45 by the back pressure present in passage 34, during the discharge stroke of the associated pump piston 18, becomes greater than the sum of the forces exerted by the associated spring 48 and the fluid pressure in biasing chamber 46, and the accumulator piston moves in the accumulator volume-increasing direction. Movement of this piston continues until the spring force increases sufliciently to again establish a condition of force equilibrium. During the time that an accumulator piston 45 is moving, the fluid displaced by the associated pump piston 18 is delivered into the accumulator chamber through passage 34, and grooves 47; the check valve 42 remaining closed. When equilibrium is established, check valve 42 opens and the fluid displaced by pump piston 18 during the remaining portion of its discharge stroke is delivered to the discharge port 13. When the piston 18 commences to move on its suction stroke, check valve 42 closes and the fluid collected in the accumulator chamber is returned to the working chamber 19 through grooves 47, and passage 34.

It will be apparent that as discharge pressure continues to rise and the pressure in the biasing chambers 46 decreases, the distance the accumulator piston must shift during each discharge stroke in order to maintain equilibrium becomes increasingly greater. Therefore, an increasingly greater portion of the fluid displaced by each pump piston is directed into the accumulator chamber and the effective displacement of the pump (i.e., the rate of delivery from discharge port 13) decreases progressively. Because of the presence of restrictor 67, the pressure at port 53 of the control valve, and consequently the pressure in biasing chambers 46, changes rapidly with movement of valve plunger 57. As a result, the slope of the characteristic displacement versus discharge pressure curve for this pump is steep.

When the biasing chamber pressure drops so low that each accumulator piston 45 approaches its limit of movement in the accumulator volume-increasing direction and substantially the entire displacement of the pump piston 18 is being delivered into the accumulator, ports 69 are uncovered and fluid is permitted to flow from the accumulator chambers to the by-pass port 14 through annular groove 68 and passage 71. This circulation of fluid from the inlet port 12 to the by-pass port 14 serves to cool the pump in the absence of discharge from port 13. Since this cooling flow is produced at a time when the pressure in the biasing chambers 46 is approximately equal to inlet pressure, little energy is consumed and pump efiiciency is not materially aflected.

It will be obvious, from the preceding description, that should the discharge pressure now decrease (as a result of an increase in demand for high pressure fluid), the amount of fluid collected in the accumulator chambers during the discharge strokes of the pump pistons will decrease and consequently the effective displacement of the pump will increase.

It should be observed that during zero displacement operation, the pressure in passages 34 and in working chambers 19 is determined by springs 48 and therefore it is quite low. As a result of this unloading of the pump pistons 18, the mechanical losses in the pump are quite small.

When the pump is used to supply fluid to a tight system, the embodiment wherein the springs 48, 48' are identical is satisfactory. However, when system leakage is relatively great, it is better to employ one spring 48 (or 48) which has a rate higher than the rates of all the other springs. In this Way, the leakage requirement can be met by one piston 18 (or 18) while all the others are unloaded.

As stated previously, the drawings and description relate only to a preferred embodiment of the invention. Since many changes can be made in the structure of this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

1. In a reciprocating piston pump of the type including a housing containing a plurality of cylinder bores, a piston reciprocable in each cylinder bore and defining therewith a pump working chamber, inlet and discharge passages forrned in the housing and communicating with each pump working chamber, and a spring-biased check valve located in each discharge passage for preventing reverse flow from that passage to the pump working chamber, the improvement which comprises means defining a plurality of variable volume accumulator chambers, one accumulator chamber communicating with each pump working chamber and each accumulator chamber having a wall which is movable in chamber volumeincreasing and chamber volume-decreasing directions; springs, one reacting between the housing and each accumulator chamber wall and urging the wall in the chamber volume-decreasing direction; a plurality of biasing means, one associated with each wall for exerting a force on the wall which urges it in the chamber volumedecreasing direction; and common control means associated with the biasing means for varying the force which each exerts on the associated chamber wall between two values, one of the values being sufficiently high that the pressure in each working chamber required to open the spring-biased check valve is ineifective to shift the accumulator wall an appreciable distance in the chamber volume-increasing direction and the other value being sutficiently low that the working chamber pressure required to open the check valve is eifective to shift the accumulator wall an appreciable distance in the chamber volume-increasing direction.

2. In a reciprocating piston pump of the type including a housing containing a plurality of cylinder bores, a piston reciprocable in each cylinder bore and defining therewith a pump working chamber, inlet and discharge passages formed in the housing and communicating with each pump working chamber, and a spring-biased check valve located in each discharge passage for preventing reverse flow from that passage to the pump working chamber, the improvement which comprises means defining a plurality of accumulator bores; an accumulator piston reciprocable in each bore and dividing it into an accumulator chamber and a biasing chamber, the volumes of these chambers being varied in reverse senses as the piston moves in opposite directions; springs, one biasing each accumulator piston in the accumulator chamber volume-decreasing direction; passages, one connecting each accumulator chamber with one pump working chamber; a control valve having an inlet port connected with the discharge passages, an exhaust port connected with the inlet passages, an outlet port connected with the biasing chambers, and a movable member which is shiftable in opposite directions from a mid position in which all three ports are interconnected to graduate in reverse senses the restrictions to flow between the inlet and outlet ports and between the exhaust and the outlet ports, respectively; a control spring biasing the movable member in that direction which increases the restriction to flow between the outlet and exhaust ports; and a control motor having a working chamber and a movable element subject to the pressure in that chamber and connected with the movable member of the control valve for shifting it in the opposite direction against the bias of the control spring.

3. The improvement defined in claim 2 in which the working chamber of the control motor communicates with the discharge passage.

4. The improvement defined in claim 3 in which the connection between the inlet port of the control valve and the discharge passage contains a flow restrictor.

5. In a reciprocating piston pump of the type including a housing containing a plurality of cylinder bores, a piston reciprocable in each cylinder bore and defining therewith a pump working chamber, inlet and discharge passages formed in the housing and communicating with each pump working chamber, and a spring-biased check valve located in each discharge passage for preventing reverse flow from that passage to the pump working chamber, the improvement which comprises means defining a plurality of accumulator bores; an accumulator piston reciprocable in each accumulator bore and defining therewith a variable volume accumulator chamber; passages, one connecting each accumulator chamber with one pump working chamber; springs, one reacting between the housing and each accumulator piston for urging it in the chamber volume-decreasing direction; a plurality of pressure-responsive biasing means, one associated with each accumulator piston for urging it in the chamber volume-decreasing direction; and common control means associated with the pressure-responsive biasing means for subjecting each to a control pressure that varies between one value which is sufiiciently high that the pressure in each working chamber required to open the spring-biased check valve is ineliective to shift the accumulator piston an appreciable distance in the chamber volume-increasing direction and a second value which is sufficiently low that the working chamber.pressure required to open the check valve is efiective to shift the accumulator piston an appreciable distance in the chamber volume-increasing direction.

6. The improvement defined in claim 5 including a by-pass port formed in the housing; and by-pass passages, one connecting the by-pass port with each accumulator bore, the intersection of the by-pass passage and the bore being so positioned that the accumulator piston interrupts communication between the by-pass passage and the accumulator chamber when the volume of that chamber is a minimum and opens communication between that passage and the accumulator chamber as it moves in the chamber volume-increasing direction.

7. In a reciprocating piston pump of the type including a housing containing a plurality of cylinder bores, a piston reciprocable in each cylinder bore and defining therewith a pump working chamber, inlet and discharge passages formed in the housing and communicating with each pump working chamber, and a spring-biased check valve located in each discharge passage for preventing reverse flow from that passage to the pump working chamber, the improvement which comprises means defining a plurality of accumulator bores; an accumulator piston reciprocable in each accumulator bore and defining therewith a variable volume accumulator chamber; passages, one connecting each accumulator chamber with one pump working chamber; springs, one reacting between the housing and each accumulator piston for urging it in the chamber volume-decreasing direction; a plurality of pressure-responsive biasing means, one connected with each accumulator piston for urging it in the chamber volume-decreasing direction; common means associated with the pressure-responsive biasing means for subjecting each to a control pressure which is sufiiciently high that the pressure in each working chamber required to open the spring-biased check valve is ineffective to shift the accumulator piston an appreciable distance in the chamber volume-increasing direction; and means associated with the common means and operable in response to a rise in pump discharge pressure above a predetermined value for progressively decreasing the control pressure to a value which is sufiiciently low that the working chamber pressure required to open the check valves is effective to shift the accumulator pistons an appreciable distance in the chamber volume-increasing direction.

References Cited in the file of this patent UNITED STATES PATENTS 684,806 Enzinger Oct. 22, 1901 2,711,697 Gibbs June 28, 1955 2,730,952 Whiifen Jan. 17, 1956 2,780,173 Herbrich Feb. 5, 1957 2,956,501 Norlin Oct. 18, 1960 FOREIGN PATENTS 319,758 Italy July 19, 1934 1,183,888 France July 15, 1959 

